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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <4EDC79DC-0C32-40FD-9C35-164C7A077922@oracle.com>
References: <4EDC79DC-0C32-40FD-9C35-164C7A077922@oracle.com> <20230316152618.711970-1-dhowells@redhat.com> <20230316152618.711970-28-dhowells@redhat.com> <3DFBF27C-A62B-4AFE-87FD-3DF53FC39E8E@hammerspace.com>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     dhowells@redhat.com, Trond Myklebust <trondmy@hammerspace.com>,
        Matthew Wilcox <willy@infradead.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Jeffrey Layton <jlayton@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Anna Schumaker <anna@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [RFC PATCH 27/28] sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
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Date:   Thu, 16 Mar 2023 17:28:02 +0000
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Chuck Lever III <chuck.lever@oracle.com> wrote:

> That means I haven't seen the cover letter and do not have any
> context for this proposed change.

https://lore.kernel.org/linux-fsdevel/20230316152618.711970-1-dhowells@red=
hat.com/

> We've tried combining the sendpages calls in here before. It
> results in a significant and measurable performance regression.
> See:
> =

> da1661b93bf4 ("SUNRPC: Teach server to use xprt_sock_sendmsg for socket =
sends")

The commit replaced the use of sendpage with sendmsg, but that took away t=
he
zerocopy aspect of sendpage.  The idea behind MSG_SPLICE_PAGES is that it
allows you to do keep that.  I'll have to try reapplying this commit and
adding the MSG_SPLICE_PAGES flag.

> Therefore, this kind of change needs to be accompanied by both
> benchmark results and some field testing to convince me it won't
> cause harm.

Yep.

> And, we have to make certain that this doesn't break operation
> with kTLS sockets... do they support MSG_SPLICE_PAGES ?

I haven't yet tackled AF_TLS, AF_KCM or AF_SMC as they seem significantly =
more
complex than TCP and UDP.  I thought I'd get some feedback on what I have
before I tried my hand at those.

David